The invention relates to a method of producing a wire-drawing die. In the method, a core is mounted in an annulus which is then secured in a metal housing. The core is then provided with a drawing passage. The core may consist of a material such as polycrystalline diamond, polycrystalline cubic boron nitride or a mixture thereof.
In this connection, "polycrystalline diamond" should be understood to mean an aggregate of synthetic diamond. Polycrystalline diamond is commercially available under various designations (e.g. "Compax"--General Electric Company, USA, and "Syndite"--De Beers Industrial Diamond Division). On delivery, the aggregate of synthetic diamond is usually attached to a cemented carbide substrate (for example WC+Co). The substrate may be flat or annular. In the latter case, the aggregate of synthetic diamond fills the opening in the annular substrate.
The annular substrate filled with synthetic diamond is usually used for the production of wire-drawing dies. However, the heat conductivity of cemented carbides is relatively low, which is a drawback for this use. It is also necessary to use special tools to produce each individual size of the synthetic diamond/cemented carbide annular combination. Sometimes the cemented carbide annulus must be treated, for example by means of shrinking or pressing, in order to secure it in a metal housing.
Polycrystalline cubic boron nitride is also commercially available (e.g. as "Amborite"--De Beers Industrial Diamond Division, and "Barozon CBN"--General Electric Company USA).
Wire-drawing dies having an aggregate of synthetic diamond mounted in a cemented carbide annulus are commercially available. Usually the core, which is mounted in a cemented carbide annulus, is fitted in a metal housing by means of a shrinking or pressing operation. For one type of wire-drawing die, the polycrystalline diamond core with a cemented carbide annulus is provided with an envelope of brass (e.g. 37.8% by weight of Zn, 3.4% by weight of Pb, remainder Cu) in such a way that the raised edges of the envelope are just clear from the drawing passage after the latter has been formed. The core mounted in the annulus is fitted by cold pressing in a metal housing consisting of austenitic chromium-nickel steel. A plug of austenitic chromium-nickel steel is also pressed into the housing.